This invention relates to a switched mode drive circuit and method for an inductive component. The invention more particularly, but not exclusively, relates to buck, boost and push-pull drive circuits.
Drive circuits comprising a first switch having first and second terminals, a second switch having first and second terminals and wherein a terminal of the first switch, a terminal of the second switch and one end of an inductive component to be driven are connected to one another at a common node are known in the art. In push-pull configurations, transistors are used as the first and second switches and in buck, boost and buck-boost configurations, a diode is used as one of the switches.
In all these configurations, an energy storage device is connected over the terminals of the first and second switches that are not connected to the common node. In push-pull and buck configurations, the energy storage device comprises a DC power supply. In a boost configuration the energy storage device comprises an output capacitor and in a buck-boost configuration, the energy storage device may comprise a DC power supply and an output capacitor connected in series.
During normal operation, the switches are driven to be on and off in alternating relationship—that is when the first switch is on, the second switch is off, and vice versa. However, it is well known that it may happen that both the first and second switches are on at the same time, so that the energy storage device is short-circuited. This may result in large currents which may cause damage, such as damage to the switches.
Conventional protection circuits and methods are aimed at ensuring that the one switch is fully off, before the other switch is switched on. In push-pull configurations this may be achieved by inserting some delay between the switching off of the one transistor and before the other transistor is switched on. In buck and boost configurations a fast switching diode is normally used. In other embodiments a conventional series protection inductor comprising a magnetic core is used. As will be clear and will be described in more detail below with reference to FIG. 1, these techniques limit not only the maximum frequency of the drive circuit, but also the efficiency of the drive circuit.